Symmetrical passive RC notch filter with two cutoff frequencies for ripple reduction in chopper offset-stabilized amplifiers

Abstract

The paper presents a symmetrical passive RC notch filter with two cutoff frequencies used for ripple reduction in chopper offset-stabilized amplifiers. The filter has two cutoff frequencies: the first one is the chopping frequency itself, while the second one is the third harmonic. The rejection of the proposed filter is 60 dB around the cutoff frequencies. The chopping frequency is correlated with the cutoff frequencies by using a current-driven oscillator and a bias circuit using the same type of resistor as the filter itself. A circuit using this technique was fabricated, achieving a low-frequency noise performance of 1.3 μV pp .

Optimizing frequency compensation in chopper offset-stabilized amplifiers with symmetrical RC notch filters

“…These values are somehow lower than the 60 dB obtained in [7] for a similar filter having the second cutoff frequency at the third harmonic, but still quite close.…”

“…A new approach of filtering was described in [7] and included within the chopper offsetstabilized operational amplifier shown in Fig. 1.…”

“…The second cutoff frequency was revised from the third harmonic used in [7] to reduce the settling time.…”

“…1 illustrates that only two synchronized clock signals, Phase 1, and Phase 2, are needed, thus simplifying the digital controls, and minimizing the number of glitches within V OUT , as presented in [7].…”